There are known flash images like one shown in FIG. 22 that images of a moving object are picked up by a fixed camera and how the object moves is expressed in one image (picture). According to film cameras, strobe flashing is carried out plural times relative to a moving object during a long-time exposure to generate such a flash image. In recent days that digital cameras become widespread, flash images can be generated through an image processing by a computer in cameras.
In generating a flash image, images of a moving object are picked up by continuous image-pickup with the angle of view of a digital camera and a direction thereof being set at constant. When images are picked up with the digital camera being held in hands, because the digital camera slightly moves, a change in the angle of view among continuously picked-up frame images may be caused. In a case in which the depth of a background of an object (a moving object) is large, when the displacement between the frame images is large, because of occlusion, a difference in a background area is created which must be originally stay at the same place among the frame images. If such a difference is large, the background part may be falsely recognized as the moving object. As a result, the background part is duplicated (duplicatingly synthesized) over a generated flash image.